Active molecules extraction and conversion from plant biomass: Salts as green catalysts and solvents

Global awareness of the inevitable depletion of fossil carbon resources, the need to fight climate change, and the reduction of greenhouse gas emissions leads to implementing sustainable alternatives to fossil carbon. The sustainable development strategy is based on biomass integration with good savings and better management. Natural molecules including cellulose, hemicellulose and lignin can be extracted from this biomass and processed to produce energy and biobased products to replace synthetic products.
This work fits into the framework of lignocellulosic biomass valorisation and the ecological solvent use, particularly salts, which are among green chemistry principles.
First, the entire chemical composition and phytochemical characterisation of agri-food side-products, marine residue, and wild grass feedstock have been evaluated. These residues were classified into three new categories, and their potential as inflows in biorefining operations was studied. Results showed that liquid biofuels and platform chemical production reached more than 2 to 9 million tons annually.
Furthermore, the physicochemical changes of pretreated biomasses under hydrothermal conditions combined with inorganic salts were evaluated. Hemicellulose extraction is improved by increasing the salt (NaCl, KI) concentration, reaching 93%. Oligosaccharide and degraded products formation were also increased, reaching 19.7 % and 24 %, respectively. The followed NaOH treatment efficiently extracted cellulose and lignin with high yields and purities. Moreover, it also improved enzyme accessibility for cellulose conversion into glucose by seven times more.
Besides, to better understand dehydrated product formation (5-HMF, 2-F, lactic acid, formic acid and levulinic acid) produced from carbohydrates, the monosaccharides D-xylose and D-glucose were dehydrated in seawater and salts solution. The introduction of NaCl (1.19 M) promoted the conversion of D-xylose to 2-F from 28% to 44% compared to deionised water. In seawater, 5-HMF production from D-glucose was raised to 30%, and lactic acid production increased by 10 % for both monosaccharides.
Moreover, the potential of DESs solvent for lignocellulosic matrice fractionation and lignin recovery was explored. An ultrafast process comprising microwave-DES combination efficiently extracted lignin with a purity exceeding 70 % in 60 s at 800 W.
This research demonstrates the application of green chemistry principles using renewable raw materials, bioprocesses (steam explosion, microwave, hydrothermal reactor) and green catalysts (inorganic and organic salts) to produce safer bioproducts. This work supports the possibility of exploiting Mediterranean biomass, available in huge quantities at low cost and under-exploited, for bioproducts production (fuels, chemicals, and biogas).